Cuban authorities have since released few details of the revolutionary leader's exact condition, but insist he has been recovering steadily.
"I have been in contact with him a lot ... and the process of recovery continues going very well," Alarcon said.
He stressed, though, that it was necessary for Raul, Cuba's defense minister and number two, to remain at the helm for the time being.
Alarcon, however, insisted that did not mean Fidel Castro was out of the loop.
"Fidel has been and is very involved, very connected, very active in the important decisions that have been taken in the country," he said.
He acknowledged though that world's longest-serving head of state could not be as involved as in the past, "since he has to devote much of his time to his physical recovery."
Alarcon said that how long it takes Castro to resume his full functions "depends on he and his doctors."
Since Castro stepped aside in July, he has appeared six times in film footage to show he was recuperating, the most recent on January 30.
In a transcript of a telephone conversation published by Cuba's official Granma newspaper on Wednesday, Castro told his friend Hugo Chavez, the Venezuelan president, he felt "very well."
Chavez also suggested Castro would soon be ready to resume his activities and hinted at a holding meeting together with Evo Morales, Bolivia's president, in April.
The Venezuelan leader has visited Castro, and talked to him on the telephone, on several occasions since July.